The present disclosure relates to the use of one or more ion beams to prepare materials for microscopic observation or spectroscopic analysis. Microscopic observational techniques include, but are not limited to, optical light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and reflection electron microscopy (REM). Spectroscopic analysis techniques include, but are not limited to, x-ray microanalysis, reflection electron energy-loss spectroscopy (REELS), electron back-scattered diffraction (EBSD), x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Materials to be viewed under any microscopic technique may require processing to produce a sample suitable for microscopic examination.
Microscopies making use of electrons to probe and image samples are important techniques for studying the detailed microstructure of many materials. The preparation of these samples for observation is very demanding. The goals of sample preparation are: preserve as many salient sample features as possible; avoid artifacts that might change, lose, or add additional information; render the sample stable for examination, in an observational environment, that may be carried out within a range of temperatures, vacuum conditions, and charged and neutral particle fluxes; and, to enable the observation of the sample as near to its natural state as possible.
Ion beam milling of a material can produce samples that are well suited for microscopic examination. Ion beam milling may be employed during sample preparation to thin, smooth, expose, and etch regions of interest in the sample for later microscopic study. An ion beam irradiating device may generate, accelerate, and direct a beam of ions toward a sample. The impact of ions on the sample will sputter material away from the area of ion impact. The sample surface may be polished by the ion beam to a substantially smooth condition, further enhancing observational properties of the sample. Regions of interest in the sample may be exposed and polished by the use of ion beams, thus making a suitable observational sample from the material under investigation. Furthermore, a sample may be etched by the action of one or more ion beams and may thereby be prepared to accept a coating on its surface.
Coating a sample with a carefully chosen coating material can produce samples with observational characteristics better than those achievable from the intrinsic properties of the sample material alone. Thin coatings of carbon, metals such as: gold; chromium; platinum; palladium; iridium; tungsten; tantalum, and other compounds can be used to coat a prepared sample and thereby produce changes in: conductivity; charge accumulation during observation; edge resolution during observation; thermal damage; secondary electron emission; backscattered electron emission; and mechanical stability.
Ion beam systems used to mill samples destined for microscopic analysis typically expose an interface, or underlying structure of interest, or produce a sample with an electron-transparent region. Many of these systems have rotating samples and fixed beams, so that the beams may strike the sample from multiple directions. This provides for more uniform milling of a sample by compensating for the shadowing of certain regions that may happen due to the nonuniform topology of the sample surface. In the typical system used for ion beam milling, material is removed most quickly from the sample by the ion beam in the region of the sample described by the intersection of the rotation axis of the sample with the center of the ion beam itself.
Important considerations to users of ion beam milling techniques include: reducing or minimizing the time and effort the user is occupied in processing the sample; reducing or minimizing the number of steps where delicate samples are directly handled and at risk for damage, such as during mounting to sample holders for processing or analysis; reducing or minimizing the time and effort the user is occupied transferring the sample into the ultimate analysis equipment (imaging or spectroscopy) and aligning the coordinates of the prepared sample region to the ultimate analysis equipment prior to analysis; ensuring high quality and high probability of success in processing and imaging the sample; reducing or minimizing the time that the ion milling equipment and sample mounting equipment are occupied for each sample; and ensuring high-quality microscopy observation of the sample during sample mounting and ultimate analysis by reducing the working distance required between the sample and the objective or probe-forming lens used for observation.
Important considerations with respect to coating a sample with a coating material that enhances its properties during subsequent microscopic observation include: improving the spatial uniformity of coating; reducing the time required to coat a sample; improving the repeatability of the coating step; controlling the coating thickness; and improving the efficiency of the coating step.
In consideration of the foregoing points, it is clear that embodiments of the present disclosure confer numerous advantages, and are therefore highly desirable.